What works best will depend on a number of factors. A large antenna on roof will be a short antenna in terms of the length of the radio wave you are listening to. But that is not an issue with a radio like the Yupti, which is prone to over loading & one advantage of a antenna away from & above the house is that the electrical noise of the house is not an issue. However a few meters of wire strung around a room works for most of us. Do not over load the Yupti, it is a jack of all trades, master on none & it is designed to work on a short antenna & thus it overloads really quickly if you put up a decent antenna & then, instead of receiving more, you receive less. I have a number of portable radios & only use around 5 meters maximum with them & looking at other members of the British DX Club (An SWL club) most others only use short wires on their portable radios too.

Also enable the attenuator when using a long wire or large antenna for SWL as it will improve the situation no end, I used to have to do this on mine and as Alan said they overload really easy so it will help with that issue. They are not too bad for SW and one of the best jack of all receivers.